1. Technical Field of the Invention
The present invention relates to a cooled turbine blade provided with a film cooling hole to form a thin film of cooling air on the surface of a turbine member.
2. Description of the Related Art
FIG. 1 is a typical structural view of a turbo jet engine provided with an air intake 1, a compressor 2, a combustor 3, a gas turbine 4, an after-burner 5, and a jet nozzle 6. In this turbo jet engine, air is introduced from the air intake 1 and is compressed in the compressor 2; and, in the combustor 3, fuel is fired to produce a high-temperature combustion gas, the gas turbine 4 is driven by the produced combustion gas, compressor 2 is driven by this gas turbine 4, the after-burner 5 burns the fuel again using an exhaust gas from the turbine, the high-temperature fuel exhaust gas is expanded in the jet nozzle 6 and jetted out backwards, thus a thrust is generated. This configuration is same in a jet engine other than the turbo jet engine.
It is known in the prior art that with the aforementioned jet engine or any other gas turbine, a higher turbine inlet temperature can be applied by cooling the turbine blade of the gas turbine, thereby the performance of the gas turbine can be improved. Consequently, in addition to conventional convection cooling, impinge cooling, film cooling, transpiration cooling, or any other cooling means are provided to cool the turbine blades.
FIG. 2 is a sectional view showing an example of a conventional cooling turbine blade. In this example, a cooling air flow passage is provided in the interior of a turbine blade 4a, the cooling air that passes through this cooling air passage, impinge-cools the inner surface of the turbine blade 4a and blows out through air cooling holes 7 (film cooling holes) disposed on the back and belly sides of the turbine blade 4a and forms a thin film of cooling air on the surface of the turbine blade 4a, thus the air cools the film (for an example, see Patent Literature 1).
In this application, the back side means a suction side of a blade, and the belly side means a pressure side thereof.
[Patent Literature 1]
Unexamined Japanese patent publication No. 28203, 1996
The turbine blade rotates at a high speed, and the higher the speed, the more efficiently the blade generates power. However, the rotating speed is limited by the strength of the turbine disk that supports the blade. That is, most of the power applied to the disk comes from a centrifugal force acting on the rotating turbine blade, so eventually the total weight of the turbine blade determines a limit of rotating speed. Therefore, the lighter the weight of the turbine blade is, the more advantageous it is. However, because a means for cooling the turbine blade must be provided, a passage has to be provided to pass cooling air inside the blade. Therefore, the turbine blade should have a predetermined thickness. Consequently, the weight of the blade has necessarily been increased. In addition, to have good aerodynamic performance, it is required to have a large difference in flow speed between the back and belly sides of the turbine blade. That is, a considerable thickness must be provided. Therefore, it is difficult to develop a light, thin-walled turbine blade.